(1) Field of the Invention
The present invention relates to a quality evaluation method for industrial products which generate a sound in operation (for example, a motor, a compressor, an inverter, a product incorporating any of them, or a product with a mechanical operation mechanism including a gear, a cam, a slider, or the like).
(2) Description of the Related Art
With few exceptions, all industrial products generate an operation sound when in operation. Such an operation sound is emitted from functional components such as a motor and a compressor, electrical components such as an inverter, or a mechanical operation mechanism including a gear, a cam, or a slider. In a mass production line, such industrial products are evaluated using the operation sound in the middle of or after assembly.
There are the two kinds of operation sounds generated by industrial products: stationary sound and non-stationary sound. For example, some devices such as a motor or a compressor generate an operation sound having a constant sound tone, pitch, and loudness because a coil, a rotor, a vane, or a scroll of the devices rotates at a constant rate. The operation sound generated by such industrial products is called stationary sound. On the other hand, some industrial products generate an operation sound which momentarily changes in tone, pitch, or loudness depending on change in the movement of the industrial products. Such an operation sound is generated by, for example, an optical disc drive loading or unloading a medium, a car navigation system opening or closing a display, or a camera in an electric zooming operation. The operation sound generated by such industrial products is called non-stationary sound. For example, a display of a car navigation system makes no operation sound until an opening operation starts. When the display starts opening, a motor, a gear, and a cam start generating an operation sound. In most cases, an operation sound of opening of a display of a car navigation system changes from the beginning toward the end because engagement of gears or a rotational speed of a motor of changes. It is thus considered difficult to evaluate quality of industrial products based on non-stationary sound in comparison with evaluation based on stationary sound.
Evaluation of quality of industrial products based on an operation sound is usually made through a sensory evaluation using a human sense of hearing. Criteria of the evaluation depend on the sense of evaluator and vary among them. It is thus difficult to quantitatively evaluate quality of industrial products. The criteria of the evaluation may vary even for an evaluator, depending on the evaluator's body condition or environment, so that such evaluation using a sense of human hearing proves to be far from a quantitative evaluation. Thus, there have been attempts to automate evaluation of quality of industrial products based on operation sounds.
In one of conventional methods of automated quality evaluation of industrial products based on operation sound, quality is evaluated with reference to a threshold set for sound pressures of frequencies measured by sound-level meter (for example, see Japanese Unexamined Patent Application Publication No. 2006-126141 (Patent Reference 1)). FIG. 25 illustrates the conventional quality evaluation method for industrial products based on operation sound disclosed in Patent Reference 1.
As shown in FIG. 25, in a conventional method of evaluation of industrial products, an evaluation parameter is set for each frequency band in a frequency space.
However, in the conventional method, thresholds (evaluation parameters in FIG. 25) are set only for the frequency space, so that only stationary sounds generated by industrial products are evaluated. In this case, it is difficult to evaluate quality of industrial products which generate a non-stationary sound, which momentarily changes.
In addition, in the conventional evaluation method, a product is rated as a conforming product as long as a sound generated by the product is at a threshold sound pressure level or lower because quality is evaluated only based on sound pressure levels, which are indices for physical loudness of sound. However, some products should be rated as a defective because of tone of its sound even when the sound pressure level is at a threshold or lower. It is therefore difficult to effectively evaluate quality of industrial products only based on sound pressure levels.
The present invention, conceived to address the problem with conventional techniques, has an object of providing an evaluation method based on sound with a focus on tone.